The clause on common constitutional traditions belongs both to the world of the «law in books» and to the space of the «law in action». This terminology — «constitutional traditions common to the Member States» — has been frequently used by the Court of Justice of the European Union, to refer not only to constitutional provisions, but also to their history and implementation. However, its scope is limited by the TEU, although from certain points of view, the clause may be open to manipulation, as recently emerged in the CJEU s case law. Moreover, the common constitutional traditions are not an autono- mous source of law, also because they are always used in combination with other sources to lend more authority to the latter. This partially explains why, although the clause has proven extremely popular, it has remained “empty”, in several decisions receiving only a passing reference.